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## Homework Statement

find parametric equations for the semicircle x^2+y^2=a^2, y>0

using as parameter the slope t=dy/dx of the tangent to the curve at (x,y)

## Homework Equations

## The Attempt at a Solution

well i know that to parametrize a circle i would use x=acost and y=asint for 0<=t<=2pi

so i guess if i just want the top half i would use 0<=t<=pi ? but I am not sure how to use the derivative of y=sqrt(a^2-x^2) to parametrize the curve

i went ahead and found dy/dx to be 1/2(a^2-x^2)^(-1/2)*-2x or -x/sqrt(a^2-x^2)

i don't know what to do next...